This interface also allows for commands to be used. See the
"Filter commands" section for more details.
+ As a speed up, since processing strings can't be quite expensive
+ and requires a check of all functions registered to tracing, instead
+ an index can be written into this file. A number (starting with "1")
+ written will instead select the same corresponding at the line position
+ of the "available_filter_functions" file.
+
set_ftrace_notrace:
This has an effect opposite to that of
We can see that there's no more lock or preempt tracing.
+Selecting function filters via index
+------------------------------------
+
+Because processing of strings is expensive (the address of the function
+needs to be looked up before comparing to the string being passed in),
+an index can be used as well to enable functions. This is useful in the
+case of setting thousands of specific functions at a time. By passing
+in a list of numbers, no string processing will occur. Instead, the function
+at the specific location in the internal array (which corresponds to the
+functions in the "available_filter_functions" file), is selected.
+
+::
+
+ # echo 1 > set_ftrace_filter
+
+Will select the first function listed in "available_filter_functions"
+
+::
+
+ # head -1 available_filter_functions
+ trace_initcall_finish_cb
+
+ # cat set_ftrace_filter
+ trace_initcall_finish_cb
+
+ # head -50 available_filter_functions | tail -1
+ x86_pmu_commit_txn
+
+ # echo 1 50 > set_ftrace_filter
+ # cat set_ftrace_filter
+ trace_initcall_finish_cb
+ x86_pmu_commit_txn
Dynamic ftrace with the function graph tracer
---------------------------------------------
}
static int
+add_rec_by_index(struct ftrace_hash *hash, struct ftrace_glob *func_g,
+ int clear_filter)
+{
+ long index = simple_strtoul(func_g->search, NULL, 0);
+ struct ftrace_page *pg;
+ struct dyn_ftrace *rec;
+
+ /* The index starts at 1 */
+ if (--index < 0)
+ return 0;
+
+ do_for_each_ftrace_rec(pg, rec) {
+ if (pg->index <= index) {
+ index -= pg->index;
+ /* this is a double loop, break goes to the next page */
+ break;
+ }
+ rec = &pg->records[index];
+ enter_record(hash, rec, clear_filter);
+ return 1;
+ } while_for_each_ftrace_rec();
+ return 0;
+}
+
+static int
ftrace_match_record(struct dyn_ftrace *rec, struct ftrace_glob *func_g,
struct ftrace_glob *mod_g, int exclude_mod)
{
if (unlikely(ftrace_disabled))
goto out_unlock;
+ if (func_g.type == MATCH_INDEX) {
+ found = add_rec_by_index(hash, &func_g, clear_filter);
+ goto out_unlock;
+ }
+
do_for_each_ftrace_rec(pg, rec) {
if (rec->flags & FTRACE_FL_DISABLED)